The present invention relates to a battery pack, in which a plurality of battery modules provided with safety vents for expelling gas when the internal pressure exceeds a prescribed value are arranged in parallel, and more particularly, the present invention relates to a gas discharging device for discharging the gas expelled from the safety vents to the exterior of the battery pack.
For a driving power supply mounted in an electric vehicle, a battery pack, in which a plurality of battery modules consisting of sealed prismatic cells and provided with safety vents are arranged in parallel, is suitably used. In a battery pack of this kind, when the internal pressure of a battery module rises to a prescribed level or above due to hydrogen gas generated during charging or discharging, the safety vent operates, thereby discharging the hydrogen gas. In order to expel this hydrogen gas into the external atmosphere as a fire-prevention safety measure, a gas discharging device is normally provided in the battery pack.
A prior art gas discharging device for a battery pack is disclosed, for example, in Japanese Laid-open Patent Application No.(Hei)7-245089. Referring to FIG. 14 and FIG. 15, this battery pack 41 comprises a plurality of battery modules 43 (in this example, 24 modules) arranged in parallel in two rows (12 modules in each row, in this example). Discharge outlets 44 of the respective battery modules 43 are disposed in an alternating zig-zag fashion within the battery module groups 42a, 42b in the respective rows, these discharge outlets 44 being connected alternately to discharge gas lines 45a, 45b, 45c, 45d of the respective rows. One end of each discharge gas line is connected respectively to an air discharge section 46.
A T-shaped joint 47 is provided at the gas discharge outlet 44 of each battery module 43. Hose joints 48 are provided projecting from either end of the T-shaped joint 47, and the respective discharge gas lines 45a-45d are constituted by connecting these hose joints 48 in a sequential fashion, by means of discharge gas tubes 49.
In the example illustrated in FIG. 14, the discharge gas lines 45a and 45d, and 45b and 45c, belonging to one battery module group 42a and the other battery module group 42b, are respectively connected at the other ends thereof, by means of connecting lines 50a, 50b, so that, even if a blockage occurs in any one of the discharge gas lines 45a-45d, the gas can still be discharged from the other discharge gas line connected to same.
However, in the conventional composition of a gas discharging device as illustrated in FIG. 14 and FIG. 15, when the battery modules 43 consisting of sealed prismatic cells swell as their internal pressure rises, the interval between the gas discharge outlets 44, 44 increases, as a result of which it may happen that a discharge gas tube 49, that is sequentially connected between hose joints 48 on either end of T-shaped joints 47, is pulled away from the hose joint 48, causing the seal to become incomplete, or in some instances, the discharge gas line 45a-45d may break, and hence there is a risk of leakage of hydrogen gas.
Moreover, since the respective end sections of the discharge gas tubes 49 must be connected in a sealed state to a plurality of hose joints 48, a large amount of labour is required during assembly, and the cost becomes high.